1. Field of the Invention
The present invention relates to dezincification-resistant copper alloys methods for producing a product comprising the same, and more particularly, to a dezincification-resistant low lead brass alloy and a method for producing a product comprising the same.
2. Description of Related Art
Brass comprises copper and zinc, as major ingredients, usually at a ratio of about 7:3 or 6:4. If the zinc content of brass exceeds 20 wt %, corrosion (such as dezincification) is likely to occur. For example, when a brass alloy article is employed in the environment, zinc present on the alloy surface is preferentially dissolved and copper contained in the alloy remains on the base metal, thereby causing corrosion in the form of porous, brittle copper. Generally, if the zinc content is less than 15 wt %, dezincification is not likely to occur. However, as the zinc content increases, the sensitivity to dezincification is increased. If the zinc content exceeds 30 wt %, dezincification corrosion is more apparent.
It has been reported in literature that alloy compositions and environmental factors affect dezincification corrosion. In the context of alloy compositions, dezincification of brass with a single a phase and zinc content higher than 20 wt % gives porous copper, whereas dezincification of brass with double α+β phases begins initially in β phase and later expands to α phase when β phase is completely converted into loosely-structured copper (refer to Kuaiji Wang et al., Chinese Journal of Materials Research, Vol. 13, pages 1-8).
Because dezincification of brass severely damages the structures of brass alloys, the surface intensities of brass products produced from brass alloys are lowered such that porosity occurs on brass pipes. This significantly lowers the lifetimes of the brass products, thereby causing application problems. In particular, under the conditions of a marine climate, the lifespan of hot water products are directly affected. Therefore, AS 2345, ISO 6509, etc. are used internationally by various countries to specify the dezincification resistance of brass products. Using the standard set forth in AS 2345 established in Australia as an example, the depth of a dezincification layer formed on the surface of a brass product shall not exceed 100 μm. However, there is also literature reporting that common brass products are not likely to meet the high standards set forth in AS 2345 (referring to Casting Technology, 2007, volume 9, pages 1272-1274). Hence, the industry continues to develop dezincification-resistant copper alloys.
Regarding the formulations of dezincification resistant brass alloys, in addition to copper and zinc as major constituents, U.S. Pat. No. 4,417,929 discloses a formulation comprising iron, aluminum and silicon, U.S. Pat. No. 5,507,885 and U.S. Pat. No. 6,395,110 disclose formulations comprising phosphorus, tin and nickel, U.S. Pat. No. 5,653,827 discloses a formulation comprising iron, nickel and bismuth, U.S. Pat. No. 6,974,509 discloses a formulation comprising tin, bismuth, iron, nickel and phosphorus, U.S. Pat. No. 6,787,101 discloses a formulation comprising phosphorus, tin, nickel, iron, aluminum, silicon and arsenic at the same time, and U.S. Pat. No. 6,599,378 and U.S. Pat. No. 5,637,160 discloses adding selenium and phosphorus in a brass alloy to achieve a dezincifying effect. Moreover, CN 1906317 discloses a formulation comprising bismuth, tin, nickel and phosphorus. The alloy has an excellent dezincification-resistant corrosion property even without performing heat treatment, wherein the specific conditions of the heat treatment are not disclosed. Additionally, there is also literature disclosing adding boron, arsenic, etc. in a brass alloy to achieve a dezincifying effect (refer to Kuaiji Wang et al., Chinese Journal of Materials Research, volume 13, pages 1-8).
Conventional dezincification-resistant brasses usually have higher lead contents (most in the range from 1 to 3 wt %), facilitating cold/thermal processing of brass materials. However, as the awareness of environmental protection increases and the impacts of heavy metals on human health and issues like environmental pollution become major focuses, there is a tendency to restrict the usage of lead-containing alloys. Various countries such as Japan, the United States, etc, have progressively amended relevant regulations, applying pressure to lower lead content in the environment by particularly demanding that no lead shall leach from the lead-containing alloy materials used in products encompassing household electronic appliances, automobiles and water systems to the surroundings or drinking water, and lead contamination shall be avoided during processing. Thus, the industry continues to develop brass materials, and to find an alloy formulation that can substitute for lead-containing brasses while possessing desirable properties like good casting and mechanical properties as well as corrosion resistance.